1. Field of the Invention
The invention is directed to crystalline salt forms of an 8-azabicyclo[3.2.1]octane compound which are useful as mu opioid receptor antagonists. The invention is also directed to pharmaceutical compositions comprising such crystalline compounds, methods of using such compounds for treating or ameliorating medical conditions mediated by mu opioid receptor activity, and processes useful for preparing such compounds.
2. State of the Art
Commonly-assigned U.S. Provisional Application Nos. 60/777,962, filed on Mar. 1, 2006, and 60/841,028, filed on Aug. 30, 2006, and U.S. application Ser. No. 11/711,961 disclose 8-azabicyclo[3.2.1]octane compounds that are mu opioid receptor antagonists that are expected to be useful for treating or ameliorating medical conditions mediated by mu opioid receptor activity. In particular, the compound 3-endo-(8-{2-[cyclohexylmethyl-((S)-2,3-dihydroxy-propionyl)amino]ethyl}-8-aza-bicyclo[3.2.1]oct-3-yl)benzamide sulfate is specifically disclosed in these applications as demonstrating mu opioid receptor antagonist activity.
The chemical structure of 3-endo-(8-{2-[cyclohexylmethyl-((S)-2,3-dihydroxy-propionyl)amino]ethyl}-8-aza-bicyclo[3.2.1]oct-3-yl)benzamide (hereinafter compound 1) is shown below:

To effectively use this compound as a therapeutic agent, it would be desirable to have a solid-state salt form that can be readily manufactured and that has acceptable chemical and physical stability. For example, it would be highly desirable to have a salt form that is thermally stable, for example at temperatures exceeding about 175° C. or about 180° C., and is not hygroscopic nor deliquescent, thereby facilitating processing and storage of the material. Crystalline solids are generally preferred over amorphous forms, for enhancing purity and stability of the manufactured product.
No crystalline salt forms of compound 1 have previously been reported. Accordingly, a need exists for a stable, crystalline salt form of compound 1 that is neither hygroscopic nor deliquescent, and exhibits favorable thermal stability.